The present invention is related to variable valve train systems for use on internal combustion engines; more particularly, to devices for controllably varying the lift of valves in such engines; and most particularly, to a variable valve train device driven by an engine camshaft and employing a command link pivotably mounted on the engine head and not on the camshaft that controllably varies the lift of the intake valves to control engine load.
Internal combustion engine performance has progressed considerably in the past century. Inventions have yielded cleaner exhaust and enhanced durability, fuel efficiency, and power. Systems for varying the lift and timing of intake valves can further refine and enhance the performance of the internal combustion engine by controllably varying the volume of fuel mix supplied to the combustion chambers as a function of engine load and rotational speed. Fuel economy at part load operation can be increased by promoting more thorough combustion, reducing pumping work done by the pistons, which saps energy, deactivating cylinders, and/or by implementing a lean air/fuel ratio scheme. Matching the intake valve closing time more closely to the engine""s need can enhance driveability of a vehicle by improving engine breathing at full engine load. Moreover, if intake and exhaust events can be controlled sufficiently to vary engine load, speed, and fuel dilution over the entire spectrum of required engine operating conditions, a controllable variable valve train can obviate the need for a throttle valve and EGR valve in a gas or diesel internal combustion engine.
A range of variable valve train (VVT) actuation devices and valve timing mechanisms for enhancing engine performance are known in the automotive art, but commercial use of such devices generally has been impractical because of cost, size, and/or operating limitations which have limited their true value and practicality. For example, variable valve actuation mechanisms, as disclosed in U.S. Pat. No. 5,937,809 issued Aug. 17, 1999 to Pierik et al. and U.S. Pat. No. 6,019,076 issued Feb. 1, 2000 to Pierik et al., the relevant disclosures of both patents being incorporated herein by reference, employ a segmented single shaft crank rocker (SSCR) for operating individual or multiple engine valves by engaging a linkage with a rotary eccentric, preferably a rotary cam, to drive an oscillatable rocker cam. The disclosed SSCR mechanism has four moving components (two arms, a rocker, and a cam) and thus can be expensive to manufacture and subject to wear at a plurality of joints. In addition, in typical prior art VVT devices, springs are required to maintain contact between an input cam and a roller follower, which springs tend to increase friction and limit maximum operating speed. Further, the coordinating frames of these devices are rotatably mounted on the camshaft itself, thus creating unavoidable and undesirable frictional losses therebetween.
It is a principal object of the present invention to provide a variable valve actuation device having reduced frictional losses when compared to prior art devices.
It is a further object of the invention to provide a variable valve train device without the need for return springs to assist the device in returning to a valve-closed position.
It is a still further object of the invention to improve peak engine torque and fuel economy.
It is a still further object of the invention to controllably vary the engine load directly at the engine cylinder, thereby potentially eliminating the need for prior art throttle body and idle air control devices.
It is a still further object of the invention to provide a variable valve train device which can be economically mass-produced for commercial use in vehicles powered by internal combustion engines.
Briefly described, a variable valve train device in accordance with the invention is provided for installation on an internal combustion engine having a rotary camshaft. In a preferred embodiment, the device is capable of interfacing with a camshaft having adjacent valve-opening and valve-closing lobes for each valve. The variable valve train device is mounted on the engine head and is pivotable about the camshaft without bearing upon the camshaft to alter the timing and lift of an engine valve, typically a fuel intake valve. A command link controlling the rotational position of the apparatus with respect to the camshaft is rotationally disposed on its outer surface in a cylindrical shell bearing mounted on the engine head coaxial with the camshaft. The shell bearing is variably supported by an hydraulic lash adjuster (HLA) or an adjustable ball joint mount, or the like, such that mechanical lash in the system may be minimized. The command link includes an arcuate ring gear portion which meshes with a control shaft gear of the engine for advancing or retarding the valve timing. The command link pivotably supports a rocker assembly having first and second rollers, or sliding pad cam followers, for following the rotary motion of valve-opening and valve-closing cam lobes. The rocker assembly is pivotably linked via an output link to an output cam element, preferably a partial cam having minimal friction dependence on the camshaft, disposed between the camshaft and a conventional roller finger follower for actuating the valve. In a preferred embodiment for controlling the motion of two parallel valves at a single engine cylinder, the output link and output cam are doubled symmetrically about the command link, and a dual rocker arm cooperates with both output links for simultaneous and identical actuation of both output cams and valves. Preferably, a plurality of cylinders in an internal combustion engine are provided with an individual device in accordance with the present invention. The disclosed invention is thus capable of controlling engine load and peak engine torque directly at the cylinder head without resort to a conventional throttle and exhaust gas recirculation (EGR) valve. The invention is also useful for variably controlling the valves of other apparatus incorporating poppet-type valves, for example, compressors for air and other gases.